Theresa Kachindamoto, senior chief in the Dedza District in Central Malawi, was tired of seeing 12-year-old girls walking around with babies on their hips, according to Al Jazeera. She decided to take a stand and made 50 of her sub-chiefs sign an agreement to end child marriage in her area of authority.

“I told them: ‘Whether you like it or not, I want these marriages to be terminated,’” Kachindamoto told the news outlet.

But she didn’t stop there: She made the leaders annul any existing underage unions, and send all of the children involved back to school, according to the Nyasa Times.

While marrying under age 18 in Malawi has been illegal since early 2015, children can still be married under so-called “customary law,” meaning with parental consent and overseen by traditional leaders, reports Al Jazeera.

When four male chiefs continued to approve underage marriages, Kachindamoto suspended them as a warning to others, only hiring them back once they confirmed they had annulled the unions, according to Al Jazeera.

“First it was difficult, but now people are understanding,” she said to the outlet.

To ensure children are not being pulled out of school, Kachindamoto operates a secret network of parents to keep an eye on others. And when parents can’t afford to pay school fees, she’ll pay them herself or find someone else who can.

“I don’t want youthful marriages,” Chief Kachindamoto told U.N. Women. “They must go to school. No child should be found at home or doing household chores during school time.”

In June alone, she annulled more than 300 child marriages, according to the organization. And over the past three years, the figure reaches close to 850.

Malawi has one of the highest rates of child marriage in the world, with an alarming one in two girls married under age 18, according to Girls Not Brides. Marrying underage negatively affects girls’ development, interrupting their education and putting them at higher risk of domestic violence and early pregnancy.

In poor, rural regions like the Dedza District, rates of child marriage are particularly high, according to Unicef, and it can be hard to convince parents not to marry off their daughters in exchange for a dowry.

That’s where Chief Kachindamoto comes in.

“I talk to the parents,” she said to U.N. Women last year. “I tell them: if you educate your girls you will have everything in the future.”